The present invention relates to a method of trenching, and to a trenching apparatus, both of which are applicable in particular, but not exclusively, for cutting a trench in rock.
There are known many trenching machines for digging trenches in soil by use of a prime mover such as a crawler tractor, or a conventional tractor pulling a trailer, in which a cutting device is positioned in the trench on a boom. The main examples are a cutting rotor rotating about an axis transverse to the trench, known as a ripper cutter, or one or more cutting rotors rotating about an axis aligned along the length of the boom, generally known as a milling cutter, or a cutting device having an elongate endless support means carrying a plurality of cutting elements and trained along upper and lower runs on the boom, known as a chain cutter. Where a cutting rotor is used this is mounted on the distal end of a boom projecting forwardly and downwardly from the prime mover, relative to the direction of digging of the trench Where a chain cutter is used, this is normally mounted on a boom extending downwardly and rearwardly from the prime mover relative to the direction of cutting of the trench. In such an arrangement the elongate support member moves in a direction such that the cutting elements move downwardly around the distal end of the boom and upwardly and forwardly along the lower run of the moving elongate support member. There is normally provided in all these forms of trenching machines, a positioning device for raising and lowering the distal end of the cutting boom to vary the height of the trench. Examples of such trenching machines are found in, for example, CH-A-239495 (Entreprise de Grands Travaux SA), and WO 95/13433 (Mastenbroek and Company Limited).
All these forms of trenching machine are generally satisfactory for trench cutting in normal soil conditions, but are not suitable fur cutting trenches in rock or other hard ground materials. For cutting trenches in hard rock, labour intensive methods are generally adopted using percussion tools and explosives.
In another art unconnected with trenching, tunnelling machines for tunnelling into rock are known in which a cutting rotor known as a ball cutter protrudes forwardly on a boom from a prime mover, and is movable in a vertical plane by pivoting of the boom on the prime mover. In use the cutting rotor is lowered to the floor of the tunnel and the prime mover advances with the cutting rotor to engage the end face of the tunnel at floor level, to produce an undercut. The cutting boom is then pivoted in an upward direction by hydraulic rams so that the cutting rotor or rotors are lifted upwardly to cut a slice of material from the end face of the tunnel. The cutting boom is raised by application of a force between the cutting boom and the floor of the tunnel. In a variation of such a device, there is provided a form of chain cutter trained along upper and lower runs along the cutting boom and around the distal end of the cutting boom, for use for example in mining coal or soft stone. In such a machine the endless moving support means carrying the cutters is driven in a direction such that the cutters move upwardly around the distal end of the boom and move rearwardly along the upper run of the moving support member. Examples of both forms of tunnelling equipment are found in leaflets published in 1982 by Hawker Sidley Dosco Overseas Engineering Limited and entitled DOSCO 1982 xe2x80x9cThe Twin Boom TB600xe2x80x9d and DOSCO 1982 xe2x80x9cMark II Heavy Duty Dintheaderxe2x80x9d.
In addition to this prior art, there is disclosed in EA-A-008082 (Wallace) a machine for cutting a trench in rock by use of a ripper cutter. EP-A-0080802 also acknowledges as prior art a known trench cutting machine comprises a giant chain saw mounted on a crawler chassis and equipped with tungsten carbide teeth which literally saw away the rock. However, this machine suffers from the disadvantage that considerable bounce is generated along the saw, especially when cutting the harder rooks, and this reduces the cutting efficiency. Primarily the problem arises because of the long unsupported length of the cutting arm. There is also discussion in EP-A-0080802 of ball cutting machines such as have been described above in tunnelling, and it is said that other rock cutting machines are known for face mining operations and these comprise a rotatable cutting head carried at the end of a boom pivotably attached to a crawler chassis. However, it is said that these known machines cannot be used for cutting trenches and furthermore suffer from a similar vibration problem because they too have a long unsupported boom carrying the cutting head.
In EP-A-0080802 it is said that these difficulties are overcome by providing a machine for cutting a trench in rock having a pivoted boom with a rotatable cutting head at the distal end and a telescopic control arm extending between a mobile work platform and the end of the boom adjacent the cutting head, the telescopic control arm being an hydraulically operable ram serving to move the cutting head on an arcuate path about the pivot axis of the boom. The machine operates by the hydraulic ram applying to the cutting head a force having a major vertical component. In operation the machine is positioned to straddle the line of the trench and the boom is lowered into contact with the ground. The cutting head is rotated whilst applying force by way of the hydraulic ram to move the cutting head on an arcuate path downwardly and to remove rock from the forward end of the trench. A conveyor is positioned on the floor of the trench and the spoil is carried away. The boom is then raised and the machine moved forward and the process is repeated.
It is said that the problem of vibration and bounce with the relatively long boom is avoided because the position at which the ram is coupled to the boom adjacent to the cutting head adds to the stability of the cutting head so eliminating the vibration and bounce problems which would be expected if the ram were omitted and the cutting force was applied by the long boom. It is said that because the control arm applies the necessary loading of the cutting head, and because of the relatively short distance between the cutting head and the point of support, the problem with cutter head bounce is largely avoided.
However a disadvantage arises with this form of machine, as is acknowledged in EP-A-0080802, in that the force applied at the cutting head tends to lift the machine out of contact with the ground. It is suggested that additional ballast may carried, but it is nevertheless inescapable that there is a limit to the amount of force which can be applied to move the cutting head on its arcuate path, without the surface mounted components of the apparatus lifting from the ground surface.
It is one object of the present invention to provide a trench cutting apparatus in which the problems outlined above are avoided or reduced.
In accordance with the present invention there is provided a method of trenching comprising positioning in a trench a cutting device mounted on a prime mover movable on the ground surface above the trench; engaging an end face of the trench with the cutting device; and moving the cutting device in a vertical plane while operating the cutting device, so as to cut material from the end face of the trench; in which the method includes positioning the cutting device against the end face of the trench below the level of the ground surface, and moving the cutting device forward in the trench while operating the cutting device, so as to produce an undercut in the end face of the trench; and lifting the cutting device upwardly from the undercut by exerting A force between the cutting device and the ground surface above the trench and operating the cutting device during the upward movement so as to cut material from the end face of the trench.
It is to be appreciated that where features of the invention are set out herein with regard to a method according to the invention, such features may also be provided with regard to apparatus according to the invention, and vice versa.
In particular, there is provided in accordance with the invention trenching apparatus comprising a cutting device; mounting means for mounting the cutting device on a prime mover and for positioning the cutting device in a trench with the prime mover movable on the ground surface above the level of the trench, the cutting device being movable in a substantially vertical plane when engaged with an end face of the trench so as to cut material from an end face of the trench; in which the apparatus includes lifting means arranged to lift the cutting device upwardly while operating the putting device in cutting engagement with the end face of the trench, by exerting an upward force between the cutting device and the ground surface above the trench; and in which the cutting device comprises a boom having an elongate endless support means carrying a plurality of cutting elements and trained along upper and lower runs on the boom, the boom being mounted to project forwardly and downwardly relative to the intended direction of cutting the trench, and drive means arranged to drive the endless support means in a direction such as to carry the cutting elements upwardly around the distal end of the boom and rearwardly along the upper run of the endless support means.
In connection with yet a further aspect of the present invention, there may be provided trenching apparatus comprising a cutting device; mounting means for mounting the cutting device on a prime mover and for positioning the cutting device in a trench with the prime mover movable on the ground surface above the level of the trench, the cutting device being movable in a substantially vertical plane when engaged with an end face of the trench so as to cut material from an end face of the trench; in which the apparatus includes lifting means arranged to lift the cutting device upwardly while engaged with the end face of the trench by exerting an upward force between the cutting device and the ground surface above the trench; and control means arranged to operate the lifting mean, and the cutting device concurrently so as to lift the cutting device when in cutting engagement with the end face.
The method of the invention brings the advantage that during the upward cutting stroke the force exerted between the cutting device and the ground surface is limited only by the force generated and applied, and is not limited by potential rising of components of trenching apparatus from the ground as in the prior art where the cutting is effected on the down stroke of the cutting device. It is not necessary to provide substantial weight in the part of the apparatus on which the lifting means is mounted, as would be the case if the lifting means were pressing downwardly on the cutting device during the cutting stroke.
There will now be set out a number of preferred features of the invention. Preferably in the step of producing the undercut the cutting device is positioned to engage the end face substantially at the bottom of the trench. Also preferably the cutting device is mounted on a pivoted boom extending forwardly relative to the direction of cutting of the trench, and the said lifting step is carried out by moving the cutting device along an arcuate path defined by pivotal movement of the boom. In such an arrangement it is preferred that the step of lifting the cutting device upwardly is carried out by exerting a force between the cutting device and a region of the ground surface spaced from the axis of pivoting of the boom in a forward direction along the trench. Also preferably the step of lifting the cutting device upwardly is carried out by exerting a force between the cutting device and the ground surface in a direction substantially perpendicular to the axis of the boom, and the step of lifting the cutting device upwardly is carried out by exerting a force at the distal end of the boom adjacent the cutting device. Preferably the step of lifting the cutting device upwardly is carried out by exerting a force in a direction inclined to the vertical in a direction forwardly relative to the direction of cutting of the trench. Such arrangements add to the stability of the apparatus and allow most effective use of the upward force applied to the cutting device.
Although a number of different culling devices can be used in embodiments of the invention, it is particularly preferred that the step of cutting material from the end face of the trench is carried out by moving a plurality of cutting elements along upper and lower runs of an elongate endless support means trained along the boom, the cutting elements being driven in such a manner that at the distal end of the cutting boom the elements move in a direction upwardly around the and of the cutting boom and rearwardly along the upper run relative to the direction of cutting the trench. Such an arrangement is particularly advantageous because the cutting elements engage the undercut in a direction upwardly and rearwardly at the distal end of the boom so as to cooperate with the lifting force in bringing the cutting teeth into cutting engagement with the ground material. In the case of hard rock this allows an effective cutting action in which the movement of the cutting elements cooperates with the upward movement of the lifting means and the forward movement of the prime mover, during cutting. Also, the upper run of the elongate endless support means can be effective to carry away spoil, so that there is no need to provide a separate endless conveyor, or other means, to remove the spoil from the trench, although such an additional conveyor can be provided behind the chain cutter in some circumstances.
In alternative arrangements, the cutting device may comprise a cutting rotor mounted at the end of a boom, and the step of cutting material from the end face of the trench is carried out by rotating the cutting rotor about an axis aligned transverse to the length of the trench, or by rotating the cutting rotor about an axis aligned generally along the length of the boom.
In preferred forms it may be arranged that tho lifting means is constructed to provide a power stroke in the upward direction and a return stroke in the downward direction, and to provide a greater force in the power stroke than in the return stroke.
Although in some arrangements the lifting means may be mounted on the prime mover, it is preferred that the apparatus includes a mobile base unit spaced forwardly from the prime mover and coupled thereto for movement with the prime mover, the lifting means being mounted so as to exert the said lifting force between the cutting device and the prime mover and/or the mobile base In a particularly preferred form, the mobile base unit is coupled to the prime mover by a framework, and the lifting means includes a pivoted arm pivoted to the prime mover and extending forwardly thereof, a pivoted link coupled at one end to a forward end of the pivoted arm and at the other end to the beam of the cutting device, and a source of lifting power coupled between the arm at a position intermediate the two ends thereof and the framework at a position intermediate the two ends thereof. Preferably the lifting means includes an hydraulic ram.
In accordance with a particularly preferred feature of the invention, the apparatus may include control means programmed to carry out a predetermined operating cycle in which:
(i) the mounting means positions the cutting device against the end face of the trench at the bottom of the trench;
(ii) the prime mover moves the cutting device forwardly a predetermined distance in the trench while operating the cutting device, so as to produce an undercut in the end face of the trench;
(iii) the lifting means lifts the cutting device upwardly from the undercut through the material of the end face while operating the cutting device;
(iv) the prime mover moves the cutting device rearwardly by a predetermined distance;
(v) the lifting means lowers the cutting device to the bottom of the trench; and
(vi) the previous steps are repeated.
The base unit may consist of a structure mounted on skids which slide over the ground when propelled forwardly by the prime mover. In other arrangements the base may be mounted upon wheels, or in some cases may be mounted on a second prime mover arranged to cooperate with the first prime mover in moving the cutting device along the trench.